With the continuing emphasis on energy saving programs there is a great deal of interest in utilizing recycled paper or newsprint and grinding same for use as cellulose fiber insulation material. In the past, hammermills or rotary beaters have been employed for the purpose of grinding the paper down to a predetermined size, suitable fire retardant chemicals are added to the ground paper during or after grinding, and the insulation material is then bagged for shipment to the job site where it is fluffed up and blown into the space between ceiling joints or into the stud space in the outer walls. Since the ground cellulose is very bulky, freight rates are comparatively high and therefore it is not economically feasible to ship the finished product for any great distances. Accordingly, there is a demand for cellulose processing apparatus which can be installed relatively near the point of consumption or use which is relatively compact, highly efficient and durable requiring a minimum number of parts, can be easily assembled and installed and which requires a minimum of maintenance and attention.
The assignee of the present invention previously devised a cellulose insulation processing system in which recycled paper or newsprint was placed on an inclined conveyor belt and advanced into a restricted feed inlet at the upper end of a hammermill apparatus for gravity feed into the hammermill chamber. In the hammermill cylinder, a series of rotary beaters or hammers were mounted on a common shaft and were operated to grind the paper into fine particles but experienced serious problems associated with jamming both at the entrance and in the clearance space between the hammers and cylinder. Hammermill elements of the type described and their mounting for rotation on a common shaft are disclosed in the patent to E. A. Barcell U.S. Pat. No. 4,033,515 and assigned to the assignee of the present invention. As disclosed in that patent however the hammermill elements were intended for use in a feed grinder wherein the feed material to be ground, such as, hay was fed onto a relatively horizontal floor surface having a limited opening for gravity feed of the material into the hammermill chamber. The hammermill elements were pivotally mounted on discs and were rotatable between cross bars extending across the aperture to operate to break up the feed material and encourage its gravity feed into the hammermill chamber and specifically in such a way as to minimize slugging or jamming of the materials at the entrance to the chamber.
The considerations in processing of paper in making cellulose fiber insulation differ appreciably from those associated with the grinding of feed materials in that there is not so much of a slugging or jamming problem at the point of introduction of the paper into the hammermill chamber; however, as the paper is partially ground there is a tendency for it to jam or collect both at the entrance and along the clearance space formed along outer periphery of the chamber just outside of the outer radial ends of the hammermill elements. The partially ground material which is not small enough to pass through a discharge screen located in the wall of the hammermill chamber, if permitted to build up or collect, will not only clog the discharge area but also interfere with free rotation of the hammermill elements. Moreover, the centrifugal force of the hammermill elements will tend to prevent the partially ground material from intermixing with the main stream of materials acted upon by the hammermill elements.
As indicated eariler, hammermill systems have been employed in the past for processing materials other than paper or cellulose materials. For instance, to Reschke U.S. Pat. No. 1,975,406 discloses a feed mill employing hammermill elements in which the feed material which is not fully ground is thrown by centrifugal force into an upper cavity within the hammermill cylinder, and an adjustable deflector associated with that cavity causes that material to re-enter the main stream of feed material processed in the hammermill chamber. U.S. Letters Patent to Kramer U.S. Pat. No. 2,828,923 is directed more to a rigid type of hammermill specifically designed for reducing metal chips into smaller particles and discloses the use of a deflector within the chamber to encourage reverse flow of material which is not fully ground by the hammermill blades. Davidson U.S. Pat. No. 1,322,546 controls the ratio of the width of the inlet to the hammermill radius so as to minimize any tendency of the dust formed from material ground in the hammermill to be blown back out through the inlet. The above and other approaches in hammermill apparatus have not been found to be satisfactory, particularly in the treatment or processing of coarse paper, in overcoming the problem of slugging or jamming which occurs along the outer perimeter of the hammermill chamber particularly along the discharge area. It is therefore desirable to provide for a method and apparatus for efficiently grinding and processing clean, flat, dry newsprint into cellulose fiber insulation which will overcome the problems associated with slugging or jamming of the materials and assure continuous processing of materials at high rates of speed.